Conventionally in the treatment of immunity-related diseases such as rheumatoid arthritis and other autoimmune diseases, anti-inflammatory drugs such as steroids have been used against inflammatory reactions caused by an abnormal immune response. However, this treatment is merely a nosotropic therapy, and does not constitute a fundamental cure.
In addition, whilst abnormalities of the immune system have also been reported to be involved in the onset of diabetes and nephritis (see, for example, Non-Patent Document 1), a drug has yet to be developed capable of correcting these abnormalities.
On the other hand, development of a method for suppressing the immune response is extremely important for preventing rejection reactions during organ and cell transplants, and for treating and preventing various autoimmune diseases. However, conventionally known immunosuppressants such as Cyclosporin A (CsA) and Tacrolimus (TRL) are known to demonstrate toxicity to the kidneys and liver, and although therapies combining their use with steroids are widely used to diminish such adverse side effects, these drugs are still unable to demonstrate adequate immunosuppressive effects without causing adverse side effects.
In view of these circumstances, attempts have been made to discover compounds having low toxicity and superior immunosuppressive activity.
The following lists examples of known immunosuppressants.    (1) A compound of the general formula (a) is known as an immunosuppressant (see, for example, Patent Document 1):[Chemical Formula 1]
{in compound (a), Rx represents an optionally substituted, linear or branched carbon chain [which may have a double bond, triple bond, oxygen, sulfur, —N(Rx6)— group (wherein Rx6 represents hydrogen), optionally substituted arylene or optionally substituted heteroarylene, and may have optionally substituted aryl, optionally substituted cycloalkyl or optionally substituted heteroaryl on the end of said chain]; and Rx2, Rx3, Rx4 and Rx5 may be the same or different and represent hydrogen or alkyl}.
Although compound (a) of the prior art has as essential substituents two oxymethyl groups substituted on the same carbon atom (namely, —CH2ORx4 and —CH2ORx5), the compound of the present invention differs from compound (a) in that it has a —CH2OH group and a methyl or ethyl group substituted on the same carbon atom as the corresponding groups thereto.    (2) A compound of the general formula (b) is known as an immunosuppressant (see, for example, Patent Document 2):[Chemical Formula 2]
[in compound (b), Ry1, Ry2 and Ry3 represent a hydrogen atom or the like, W represents a hydrogen atom, an alkyl group or the like, Zy represents a single bond or an alkylene group; Xy represents a hydrogen atom or an alkoxy group, and Yy represents a hydrogen atom, an alkyl group, an alkoxy group, an acyl group, an acyloxy group, an amino group, an acylamino group or the like].
Although it is essential that compound (b) has a phenyl group in its basic backbone, the compound contained in the pharmaceutical composition of the present invention differs from compound (b) in that the corresponding group is a heterocyclic group in the form of a pyrrole group having a substituent on the nitrogen atom.
Moreover, a compound having a structure that resembles the structure of the compound contained in the pharmaceutical composition of the present invention is not disclosed whatsoever in this publication.    (3) A compound of the general formula (c) is known as an immunosuppressant (see, for example, Patent Document 3):[Chemical Formula 3]
[in compound (c), Rz1, Rz2, Rz3 and Rz4 may be the same or different, and represent a hydrogen atom or an acyl group].
Although compound (c) has two oxymethyl groups (namely, —CH2ORz3 and —CH2ORz4) substituted on the same carbon atom as essential substituents, the compound of the present invention differs from compound (c) in that it has a —CH2OH group and a methyl or ethyl group substituted on the same carbon atom as the corresponding groups thereto. In addition, although compound (c) has an essential group in the form of a phenyl group between the —(CH2)2— group and —CO—(CH2)4— group in the basic backbone thereof, the compound contained in the pharmaceutical composition of the present invention differs from compound (c) in that the corresponding group is a heterocyclic group in the form of a pyrrole group having a substituent on the nitrogen atom.    (4) A compound of the general formula (d) is known as an immunosuppressant (see, for example, Patent Documents 4 and 5):[Chemical Formula 4]
[in compound (d), R1 represents a halogen atom, a trihalomethyl group, a hydroxyl group, a lower alkyl group having 1 to 7 carbon atoms, a phenoxymethyl group or the like; R2 represents a hydrogen atom, a halogen atom, a trihalomethyl group or the like; X represents O, S, SO or SO2; and n represents an integer of 1 to 4].
Although compound (d) has two oxymethyl groups (—CH2OH) substituted on the same carbon atom as essential substituents, the compound of the present invention differs from compound (d) in that it has a —CH2OH group and a methyl or ethyl group substituted on the same carbon atom as the corresponding groups thereto. In addition, although compound (d) has a substituted phenyl group in its basic backbone as an essential group, the compound contained in the pharmaceutical composition differs from compound (d) in that the corresponding group is a heterocyclic group in the form of a pyrrole group having a substituent on the nitrogen atom.
On the other hand, a compound of the general formula (e) that has immunosuppressive activity is disclosed by the present applicant in Japanese Patent Application (Kokai) No. 2002-167382 (Patent Document 6):
[Chemical Formula 5]
[wherein R1 and R2 represent a hydrogen atom or an amino protecting group; R3 represents a hydrogen atom or a hydroxyl protecting group; R4 represents a lower alkyl group; n represents an integer of 1 to 6; X represents an ethylene group, Y represents a C1-C10 alkylene group; R5 represents an aryl group or substituted aryl group; and R6 and R7 represent a hydrogen atom].
In addition, a compound of the general formula (f) that has immunosuppressive activity is disclosed by the present applicant in Japanese Patent Application (Kokai) No. 2003-267950 (Patent Document 7):
[Chemical Formula 6]
[wherein R1 and R2 represent a hydrogen atom, an amino protecting group or the like; R3 represents a hydrogen atom or a hydroxyl protecting group; R4 represents a lower alkyl group; n represents an integer of 1 to 6; X represents an oxygen atom or an unsubstituted nitrogen atom or a nitrogen atom substituted with a lower alkyl group or the like; Y represents an ethylene group or the like; Z represents an alkylene group having 1 to 10 carbon atoms or the like; R5 represents an aryl group or substituted aryl group or the like; and R6 and R7 represent a hydrogen atom or the like].
In view of these circumstances, it is desired to discover a pharmaceutical composition having low toxicity and superior immunosuppressive activity.    [Patent Document 1] International Publication WO94/08943 (EP627406)    [Patent Document 2] International Publication WO96/06068    [Patent Document 3] International Publication WO98/45249    [Patent Document 4] International Publication WO03/029184    [Patent Document 5] International Publication WO03/029205    [Patent Document 6] Japanese Patent Application (Kokai) No. 2002-167382    [Patent Document 7] Japanese Patent Application (Kokai) 2003-267950    [Non-Patent Document 1] Kidney International, vol.51, 94 (1997); Journal of Immunology, vol. 157, 4691 (1996)